Mass Effect 2: E3 Dev Diary
This contains major spoilers. It's also a moderate amount of awesome. The Mass Effect 2 demo from E3 has been done up as a slick development video diary (below) explaining what the Bioware team is aiming to do with the game. It contains quite a bit of footage, and seems to encapsulate all the significant changes to combat, conversation, and storyline. I can't say much more that that, other than to suggest you hold back if you're trying to avoid learning too much about the game before you play it.